1. Field of the Invention
This invention relates to the treatment of hot flashes.
2. Description of the Related Art
Hot flashes
A hot flash is a momentary sensation of heat that may be accompanied by a red, flushed face and sweating. The cause of hot flashes is not known, but may be related to changes in circulation. Hot flashes occur when the blood vessels near the skin's surface dilate to cool. This produces the red, flushed look to the face. A woman may also perspire to cool down the body. In addition, some women experience a rapid heart rate or chills. Hot flashes accompanied with sweating can also occur at night. These are called night sweats and may interfere with sleep. A hot flush is a hot flash plus a visual appearance of redness in the face and neck.
According to Freedman, Semin. Reprod. Med., 2005, 23(2):117-125, hot flashes are the most common symptom of menopause. Although the appearance of hot flashes coincides with estrogen withdrawal, this does not entirely explain the phenomenon because estrogen levels do not differ between symptomatic and asymptomatic women. Luteinizing hormone (“LH”) pulses do not produce hot flashes, nor do changes in endogenous opiates. Recent studies suggest that hot flashes are triggered by small elevations in core body temperature (“Tc”) acting within a reduced thermoneutral zone in symptomatic postmenopausal women. This narrowing may be due to elevated central noradrenergic activation, a contention supported by observations that clonidine and some relaxation procedures ameliorate hot flashes. Because hot flashes are triggered by Tc elevations, procedures to reduce Tc, such as lowering ambient temperature, are beneficial. Estrogen ameliorates hot flashes by increasing the Tc sweating threshold, although the underlying mechanism is not known. Recent studies of hot flashes during sleep call into question their role in producing sleep disturbance.
Several health studies have shown that 75% of women surveyed reported having hot flashes in the period between peri- and postmenopause, with duration of symptoms for an average of 4 years. Hot flashes usually last 1 to 5 minutes, with a small percentage persisting for more than 6 minutes. The experience of a hot flash is usually described as sensations of intense heat, sweating, flushing, chills, and clamminess. Sweating is reported most frequently in the face, neck, and chest, but rarely caudally.
Peripheral vasodilation, demonstrated by increased skin temperature and blood flow, occurs during hot flashes in all body areas that have been investigated. Skin temperature increases in the digits, cheek, forehead, upper arm, chest, abdomen, back, calf, and thigh. Blood flow in the finger, hand, calf, and forearm also increases during hot flashes. These changes typically occur within the first few seconds of the reported onset of the hot flash. Sweating and skin conductance (electrical measure of sweating), also increase during hot flashes.
The change in the tone of the autonomic nervous system is responsible for the initiation of hot flashes. Norepinephrine (“NE”) released during an increase of the sympathetic tone (or decreased parasympathetic tone) of the autonomic nervous system plays a major role in thermoregulation, acting, in part, through α2-adrenergic receptors. When injected into the preoptic hypothalamus of laboratory animals, NE causes peripheral vasodilation and heat loss, followed by decline in body temperature. Furthermore, gonadal steroids modulate central NE activity. This theory is supported by clinical studies showing that the selective α2-adrenergic agonist clonidine significantly reduces hot flash frequency.
Increased shivering, induced by increased skeletal muscle tone contributes to the production of body heat. The threshold for shivering, measured using the electromyogram of skeletal muscles is lower in symptomatic postmenopausal women than in asymptomatic postmenopausal women. Some relaxation procedures that result in decreased skeletal muscle tone can help decrease hot flashes.
According to Freedman et al., J. Clin. Endocrinol. Metab., 1995, 80:2354-2358, analysis of the circadian rhythm of hot flashes (fit to a 24-hour period sine wave) demonstrated a circadian rhythm (p<0.02) of hot flashes with a peak around 6:30 p.m., lagging the circadian rhythm of Tc in symptomatic women by approximately 3 hours. The majority of hot flashes were preceded by elevations in Tc, a statistically significant effect (p<0.05). Hot flashes began at significantly (p<0.02) higher levels of Tc (36.82±0.04° C.) compared with all nonflash periods (36.70±0.005° C.). These data are consistent with the hypothesis that elevated Tc serves as part of the hot flash triggering mechanism.
Since hot flashes occur in most women with the estrogen withdrawal at natural or surgical menopause, there is little doubt that estrogens are involved in their initiation. This is supported by the fact that estrogen administration nearly eliminates hot flashes. However, estrogen withdrawal alone does not explain the etiology of this symptom because there are no correlations between hot flash occurrence and plasma, urinary, or vaginal levels of estrogens, nor are there differences in plasma levels between symptomatic and asymptomatic women. Moreover, clonidine reduces hot flash frequency without changing circulating estrogen levels, and prepubertal girls have low estrogen levels but no hot flashes. Thus, estrogen withdrawal is necessary but not sufficient to explain the occurrence of hot flashes. There is temporal correspondence between pituitary pulsation of LH and temperature changes. However, LH pulses are not the basis for hot flashes.
Therefore, increased sympathoadrenergic tone (or decreased parasympathetic tone), increased body temperature, increased electrodermal activity and increased skeletal muscle tone are conducive to hot flashes in symptomatic menopausal women.
Men may also experience hot flashes when deprived of androgens through castration (loss of both testes by accident or surgery—such as in the treatment of testicular cancer or metastatic prostate cancer) or “chemical castration” (treatment with antiandrogens or luteinizing hormone releasing hormone antagonists—usually in the treatment of metastatic prostate cancer, but occasionally for other medical conditions and in rare instances to voluntarily decrease sexual capability in the treatment of certain sexual offenders).
The Treatment of Hot Flashes
Estrogen replacement therapy. The lowered estrogen levels during menopause are treated by administering 17β-estradiol systemically using oral dosage forms, nasal sprays, and lately low-dose transdermal administration using a patch. However, estrogen replacement therapy is reported to increase the risk for breast cancer, coronary heart disease (“CHD”), thromboembolism, stroke, and dementia when administered with progesterone, and increase the risk of stroke with no reduction of CHD risk when administered alone. In light of the altered risk-benefit ratios for these treatments, they are now being given at lower doses.
Several recent studies report efficacy for certain antidepressants in the treatment of hot flashes. Paroxetine, a selective serotonin-reuptake inhibitor (“SSRI”) was shown to decrease hot flash composite scores by 62% (12.5 mg/day) and 65% (25.0 mg/day) in 165 women reporting 2-3 hot flashes/day. The placebo response rate was 37.8%. Fluoxetine is another SSRI used to treat hot flashes. In a study of 81 breast cancer survivors, a crossover analysis showed a reduction in hot flash frequency of ˜20% over the placebo condition. Venlafaxine, a serotonin-norepinephrine reuptake inhibitor, has also shown efficacy in treating hot flashes. In a study of 229 women, venlafaxine reduced hot flash scores by 60% from baseline at 75 and 150 mg/day and 37% at 37.5 mg/day compared with 27% for placebo. Side effects of these antidepressants include nausea, dry mouth, somnolence, decreased appetite, and insomnia. Besides the side effects and the slow onset of action, antidepressants require several weeks of sustained administration before achieving therapeutic effects
Clonidine ameliorates hot flashes by increasing the Tc sweating threshold. Two small placebo-controlled studies found that oral clonidine reduced hot flash frequency by 46% and transdermal clonidine reduced it by 80%. Two larger studies of breast cancer survivors receiving tamoxifen showed smaller, but significant reductions in hot flash frequency for oral and transdermal clonidine compared with placebo. However, clonidine has a slow onset of action and side effects including hypotension, dry mouth, and sedation.
Gabapentin is an anticonvulsant that binds to the α2δ subunit of a voltage-gated calcium channel, which was fortuitously found to ameliorate hot flashes in some patients. A controlled study of 59 women found a reduction of hot flash frequency of 45 vs. 29% for placebo. Side effects of gabapentin include dizziness and peripheral edema.
Nonpharmaceutical treatments include procedures to reduce Tc and ambient temperature, such as dressing in layers and using fans or air conditioning; weight loss; smoking cessation; and relaxation procedures.
Isoflavones or phytoestrogens possess estrogenic properties and are found in soy products and red clover. Black cohosh is another plant-derived substance used to treat hot flashes. A recent review of 22 controlled studies, 12 on soy and 10 on other botanical compounds, found no consistent improvement of hot flashes relative to placebo.
The Vomeronasal Organ and Vomeropherins
The vomeronasal organ (“VNO”; also known as “Jacobson's organ”) is a bilateral chemosensory organ found in most vertebrates including humans. In mammals, this organ is accessed through the nostrils (as a pair of blind tubular diverticula found at the inferior margin of the nasal septum), and has been associated with pheromone reception in most species (see generally Muller-Schwarze and Silverstein, “Chemical Signals”, Plenum Press, New York (1980); Monti-Bloch et al., J. Steroid Biochem. Mol. Biol., 1991, 39(4):573-582; Monti-Bloch et al., Ann. NY Acad. Sci., 1998, 855:373-389). The axons of the neuroepithelia of the vomeronasal organ, located supra palatinal, form the vomeronasal nerve and have direct input to the hypothalamus and limbic amygdala of the brain. The distal axons of the terminals nerve neurons may also serve as chemosensory receptors in the VNO (Stensaas et al., J. Steroid Biochem. Mol. Biol., 1991, 39(4):553-560). This nerve has direct synaptic connection with the hypothalamus.
Human pheromones delivered to the vomeronasal organ area bind to local receptors and trigger nerve signals that reach the brain inducing physiological and behavioral changes (Grosser et al., Psychoneuroendocrinology, 2000, 25:289-299). Synthetic analogs of human pheromones called vomeropherins (defined as substances that bind to receptors in the VNO), can induce robust physiological, pharmacological and behavioral changes when delivered airborne to the VNO. This information is supported by several studies in human volunteers using functional magnetic resonance imaging and positron emission tomography, showing that vomeropherins selectively activate the brain areas (hypothalamus, limbic system, cingulate gyms, anterior thalamus and prefrontal cortex) where their physiological, pharmacological and behavioral effects are integrated. 16α,17α-Epoxy-10β-hydroxyestr-4-en-3-one
U.S. Pat. No. 6,057,439, “Steroids as neurochemical stimulators of the VNO to alleviate symptoms of PMS and anxiety”, describes the use of a number of steroidal vomeropherins for the treatment of premenstrual dysphoric disorder (“PMDD”, also referred to as “premenstrual syndrome” or “PMS”) and anxiety by administration to the vomeronasal organ of an individual suffering from those symptoms. 16α,17α-Epoxy-10β-hydroxyestr-4-en-3-one is described in the patent, where it is referred to as 16α,17α-epoxyestr-4-en-10β-ol-3-one. The patent discloses the synthesis of the compound, and claims the compound and pharmaceutical compositions containing it for alleviating the symptoms of PMDD. U.S. Pat. No. 6,331,534, “Steroids as neurochemical stimulators of the VNO to alleviate pain”, describes the same steroids for alleviating pain by vomeronasal administration.
The disclosures of the documents referred to in this application are incorporated into this application by reference.